Display device and electronic apparatus

ABSTRACT

A display device is provided which offers double-sided display and achieves a thin structure and also which prevents deterioration in display quality of each of front and back display units when an illumination unit such as a backlight is shared by these display units. The display device includes a first display unit having a display surface on the front surface thereof; a second display unit having a display surface on the rear surface thereof; and a common illumination unit interposed between the first display unit and the second display unit, for illuminating both the first display unit and the second display unit with light. The illumination unit includes a light-guiding member having a first light-emitting surface opposed to the first display unit and a second light-emitting surface opposed to the second display unit, and a transflector is interposed between the second light-emitting surface of the light-guiding member and the second display unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device and an electronicapparatus, and in particular, it relates to the structure of a displaydevice suitably mounted on a portable electronic apparatus.

2. Related Art

In general, an electro-optical device such as a liquid crystal displaydevice or an electro-luminescent display device is used as a displaydevice mounted on a portable electronic apparatus. In particular, acellular phone has a compact liquid crystal display device mounted in asmall casing thereof. In recent years, a cellular phone of adouble-sided display type, having compact liquid crystal display devicesmounted on the front and back of a thin displaying portion thereof, iscommercially available on the market. Such a cellular phone has a pairof liquid crystal display devices accommodated in the displaying portionof the casing thereof so as to lie back to back and placed so as to bevisible from both the front and back sides thereof.

Many liquid crystal display devices have a structure in which abacklight serving as an illuminator is disposed behind a liquid crystalpanel. Although a reflective liquid crystal display device having nosuch a backlight is available, its application is limited since itsdisplay is invisible in dark places and at night. Although the liquidcrystal display device equipped with a backlight has a drawback inthickness, with the recent advancements in higher definition and colordisplay of a compact liquid crystal display device, most portableelectronic apparatuses have them mounted thereon. In recent years, therehas emerged a transflective liquid crystal display device equipped witha backlight and able to perform both transmissive display and reflectivedisplay.

Since a portable electronic apparatus such as the above-mentionedcellular phone has become more compact and thinner year by year, a thinliquid crystal display device is strongly desired in accordance withthis trend. In order to meet this requirement, a thinner liquid crystalpanel and a thinner backlight are under development.

Unfortunately, the above-mentioned known cellular phone of adouble-sided display type has problems in that, since a pair of liquidcrystal display devices must be accommodated in its casing so as to lieback to back, it is hard to make the casing thinner, and, even when eachof the liquid crystal display devices is made thin, the casing isthicker and heavier than a normal portable phone of a single-sideddisplay type.

One method for solving the above problems lies in that a singlebacklight is shared by the front and back liquid crystal display devicesso as to illuminate a pair of front and back liquid crystal panels.Whereas, in a cellular phone of a double-sided display type, since thedisplay areas of the front and back liquid crystal display devices aregenerally different from each other, when a single backlight is sharedby them as mentioned above, the luminance distribution of a large mainpanel is affected by an illumination action of the backlight applied ona small sub-panel disposed behind the main panel, thereby causing a riskthat a shadow of the sub-panel is reflected in a display image of themain panel and thus its display quality deteriorates.

With this background, the present invention has been made in order tosolve the above problems. Accordingly, it is an object of the presentinvention to provide a display device which offers double-sided displayand achieves a thin structure and which prevents deterioration indisplay quality of both front and back display units when an illuminatorsuch as a backlight is shared by these display units.

SUMMARY OF THE INVENTION

In order to achieve the above-mentioned object, a display deviceaccording to the present invention includes a first display unit havinga display surface on the front surface thereof; a second display unithaving a display surface on the rear surface thereof; and a commonillumination unit interposed between the first display unit and thesecond display unit, for illuminating both the first display unit andthe second display unit with light. The illumination unit includes alight-guiding member including a first light-emitting surface oppositethe first display unit and a second light-emitting surface opposite thesecond display unit, and a transflector is interposed between the secondlight-emitting surface of the light-guiding member and the seconddisplay unit.

According to the present invention, with the common illumination unitconstructed so as to illuminate both the first display unit and thesecond display unit with light, one of two illumination units can beeliminated, thereby achieving a thinner and lighter device. Also, withthe transflector interposed between the second light-emitting surface ofthe light-guiding member of the illumination unit and the second displayunit, since part of light emitted from the second light-emitting surfaceof the light-guiding member is transmitted through the transflector andis then directed towards the second display unit, while the seconddisplay unit is constructed so as to be illuminated with light, theremaining light emitted from the second light-emitting surface of thelight-guiding member can be reflected at the transflector so as to bedirected towards the first display unit. Accordingly, it is possible toplace a priority on the illumination state of the first display unit,and hence the display quality of the first display unit can be improved.

Also, with the above structure, a transflector may also be interposedbetween the first light-emitting surface and the first display unit. Inthis case, the second display unit also obtains an optical effectequivalent to that of the first display unit.

In the display device according to the present invention, the displayarea of the first display unit may extend so as to two-dimensionallyoverlap the display area of the second display unit and an area lyingoutside the display area of the second display unit. With thisstructure, since the display area of the first display unit extends soas to two-dimensionally overlap not only the display area of the seconddisplay unit but also the area outside the display area of the seconddisplay unit, light emitted from the common illumination unit towardsthe second display unit causes the display feature of the first displayunit to be optically affected due to the fact that the display area ofthe second display unit is present behind the first display unit. Hence,a shadow of the display area of the second display unit is sometimesreflected in the display surface of the first display unit. However, inthe display device according to the present invention, since thetransflector is interposed between the second light-emitting surface ofthe light-guiding member and the second display unit as described above,the optical affect caused by the second display unit can be reduced, andthus the display quality of the first display unit can be improved.

In the display device according to the present invention, thetransflector may have a light-diffusing function. With this structure,the light-diffusing function improves the evenness of illumination lightfrom the illumination unit, thereby further preventing the unevenness ofdisplay of the first display unit and the second display unit. Inparticular, when the display device has a structure in which lightreflected at the transflector is diffused, the evenness of light in thelight-guiding member is improved, and the illuminance distribution onthe first display unit is made uniform, thereby further preventing theunevenness of display of the first display unit.

In the display device according to the present invention, thetransflector may have different optical characteristics between anoverlapping portion two-dimensionally overlapping the display area ofthe second display unit, of a region two-dimensionally overlappingbetween the transflector and the display area of the first display unit,and a portion of the region other than the overlapping portion. Withthis structure, the transflector has different optical characteristicsbetween the overlapping portion and the remaining portion of the region,thereby making the optical effects of the transflector applied on thedisplay area of the first display unit different between the overlappingportion and the remaining portion. Accordingly, an optical difference,for example, a difference in luminance levels, between the overlappingportion and the remaining portion in the display area of the firstdisplay unit can be reduced, or the display quality of the seconddisplay unit can be improved.

More particularly, in the case where the transflector is disposed acrossthe entire region, assuming that the second display unit is disposedbehind the overlapping portion of the region and another unit isdisposed behind the portion other than the overlapping portion, when thetransflector is formed so as to have uniform optical characteristicsacross the entire region, a difference in reflectances between thesecond display unit and the other unit causes a black shadow or a whiteshadow of the second display unit to be reflected in the display area ofthe first display unit. Accordingly, when the second display unit andthe other unit have a difference in reflectances therebetween like this,by making the optical characteristics of the transflector differentbetween the overlapping portion and the remaining portion as mentionedabove, the foregoing black or white shadow can be less noticeable.Meanwhile, the optical characteristics of the transflector meancharacteristics such as a light reflectance, a light transmittance, alight absorptance, and a light-diffusing rate, possibly affecting thedisplay features of the first display unit and the second display unit.

In the display device according to the present invention, thetransflector is preferably a thin film composed of a reflective materialand having a thickness allowing light to be substantially transmittedtherethrough. With this structure, since the transflector is providedwith a light transmittivity by adjusting the thickness of a thin filmcomposed of a reflective material, a step such as patterning can beeliminated, thereby easily making the transflector. A thin metal film ispreferred as the reflective material. In particular, aluminum, analuminum alloy, silver, a silver alloy, and the like are preferable asthe reflective material.

In the display device according to the present invention, thetransflector is preferably a thin film composed of a reflective materialand having a plurality of fine apertures dispersed therein such thatlight is substantially transmitted therethrough. With this structure,since the transflector is provided with a light transmittivity by havingthe fine apertures dispersed in a thin film composed of a reflectivematerial, the light transmittance is accurately controlled by changingthe aperture area ratio of the apertures, for example, by changing thesize and the density of the apertures.

In the display device according to the present invention, thetransflector may be formed by a base member composed of a lighttransmissive material and a light-diffusing layer having fine particlesdispersed in the base member and composed of a light transmissivematerial having a different refractive index from that of the basemember. With this structure, the transmittivity and the reflectivity ofthe transflector can be adjusted by changing a difference in refractiveindexes between the base material and the fine particles and also bychanging the size and the density of the fine particles, and also, theunevenness of display can be prevented by the light-diffusing effects ofthe transflector. In particular, with this structure, the transmittanceof the transflector can be easily made higher.

In the display device according to the present invention, thetransflector may be formed by a base member composed of a lighttransmissive material and a light-diffusing layer having fine particlesdispersed in the base member and composed of a reflective material. Withthis structure, since light is diffused by the fine particles dispersedin the base member and composed of a reflective material, thetransmittivity and the reflectivity of the transflector can be adjustedby changing the size and the density of the fine particles, and also,the unevenness of display can be prevented by the light-diffusingeffects of the transflector. In particular, with this structure, thereflectance of the transflector can be easily made higher.

In the display device according to the present invention, a lightdiffuser may be interposed between the first light-emitting surface ofthe light-guiding member and the first display unit. With thisstructure, since the light diffuser is interposed between the firstlight-emitting surface and the first display unit, the evenness of theilluminance distribution of the illumination unit can be improved,thereby further preventing the unevenness of display of the firstdisplay unit.

Meanwhile, the light diffuser may be formed so as to have differentoptical characteristics between the overlapping portiontwo-dimensionally overlapping the display area of the second displayunit, of the region two-dimensionally overlapping the display area ofthe first display unit, and the portion of the region other than theoverlapping portion. With this structure, the unevenness of display ofthe first display unit can be further prevented.

The light diffuser may be formed by a base member composed of a lighttransmissive material and a light-diffusing layer having fine particlesdispersed in the base member and composed of a light transmissivematerial having a different refractive index from that of the basemember. Alternatively, the light diffuser may be formed by a base membercomposed of a light transmissive material and a light-diffusing layerhaving fine particles dispersed in the base member and composed of areflective material. Further alternatively, the light diffuser may beformed by a light diffusing layer composed of a light transmissivematerial and having a structure in which fine undulations are formed onthe surface thereof.

Next, an electronic apparatus according to the present inventionpreferably includes any one of the above-mentioned display devices andcontrollers for controlling the display device. Especially, as the aboveelectronic apparatus, a portable electronic apparatus is effective fromthe viewpoint of easily achieving a thin casing thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically illustrating the structure of adisplay device according to a first embodiment of the present invention.

FIGS. 2( a) to 2(e) are sectional views schematically illustrating thestructures of a transflector according to the first embodiment.

FIGS. 3( a) and 3(b) are plan views schematically illustrating thestructures of a transflector according to a second embodiment of thepresent invention.

FIGS. 4( a) and 4(b) are plan views schematically illustrating thestructures of a transflector according to a third embodiment of to thepresent invention.

FIGS. 5( a) and 5(b) are sectional views schematically illustrating thestructures of display devices according to a fourth embodiment of to thepresent invention.

FIG. 6 is a structural block diagram illustrating the structure of anexample electronic apparatus.

FIGS. 7( a) and 7(b) are perspective views schematically illustratingthe structure of a cellular phone serving as the example electronicapparatus.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, preferred embodiments ofdisplay devices and an electronic apparatus according to the presentinvention will be described in detail.

First Embodiment

Referring first to FIG. 1, a liquid crystal display device 100 accordingto a first embodiment of the present invention will be described. Theliquid crystal display device 100 includes a first display unit 110, asecond display unit 120, and an illumination unit 130.

The first display unit 110 is a liquid crystal panel and is formed suchthat substrates 111 and 112 composed of glass or plastic are bonded toeach other via a sealant 113 and have liquid crystal 114 interposedtherebetween. The liquid crystal 114 is formed so as to receivepredetermined electrical fields with electrodes formed on the innersurfaces of the substrates 111 and 112. The substrate 112 has apolarizer 115 disposed on the outer surface thereof, that is, on thefront surface side or on the observing side of the first display unit,and the substrate 111 also has the polarizer 116 disposed on the outersurface thereof, that is, on the back surface side.

The second display unit 120 is also a liquid crystal panel and is formedsuch that substrates 121 and 122 composed of glass or plastic are bondedto each other via a sealant 123 and have liquid crystal 124 interposedtherebetween. The liquid crystal 124 is formed so as to receivepredetermined electrical fields with electrodes formed on the innersurfaces of the substrates 121 and 122. The substrate 122 has apolarizer 125 disposed on the outer surface thereof, that is, on theback surface side or the observing side of the second display unit, andthe substrate 121 has a polarizer 126 on the outer surface thereof, thatis, on the front surface side.

The first display unit 110 and the second display unit 120 have theillumination unit 130 interposed therebetween. The illumination unit 130serves as a backlight. The illumination unit 130 includes a light source131 formed by, for example, a cold cathode fluorescent tube or a lightemitting diode (LED), and a light guiding plate 132 receiving lightemitted from the light source 131. The light guiding plate 132 iscomposed of a transparent material such as an acrylic resin. In theillumination unit 130, the light guiding plate 132 is a plate disposedso as to be orthogonal to an optical-axis direction of the displaydevice, and the light source 131 is disposed along a side surface of thelight guiding plate 132. The light guiding plate 132 is disposed suchthat a light incident surface 132 a serving as a side surface thereof isopposed to the light source 131, a first light-emitting surface 132 bserving as a front surface thereof, that is, an upper surface thereof inthe figure, faces the first display unit 110, and a secondlight-emitting surface 132 c serving as a back surface thereof in thefigure, faces the second display unit 120.

The light guiding plate 132 is formed so as to output illumination lightfrom the first light-emitting surface 132 b toward the first displayunit 110 and also to output illumination light from the secondlight-emitting surface 132 c toward the second display unit 120 whileallowing light received from the light source 131 to propagate therein.In the light guiding plate 132, light incident on the firstlight-emitting surface 132 b and the second light-emitting surface 132 cat an angle smaller than a critical angle is subjected to totalreflection, and light incident on the same at the critical angle orgreater is outputted outside from the first light-emitting surface 132 band the second light-emitting surface 132 c. Especially, although notshown in the figure, either or both the first light-emitting surface 132b and the second light-emitting surface 132 c may have undulatedsurfaces or scattering layers formed thereon serving as opticaldeflectors for outputting the light introduced from the light source 131along or close to the optical axis directions of the first display unit110 and the second display unit 120.

The second light-emitting surface 132 c of the light guiding plate 132and the second display unit 120 have a transflector 141 interposedtherebetween. The transflector 141 suffices to have a structure in whichpart of illumination light from the illumination unit is reflectedtowards the front surface side and at least part of the remainingillumination light is transmitted therethrough towards the back surfaceside. Also, the transflector is made from, for example, a thin metalfilm or a metal film having a large number of fine apertures dispersedtherein. In addition, the transflector 141 may be disposed while beingbonded to the rear surface of the light guiding plate 132 or may beformed from a sheet or a plate independent of the light guiding plate132. Meanwhile, although the transflector according to the presentinvention suffices to be interposed between the second light-emittingsurface 132 c of the illumination unit 130 and the second display unit120 and has no limitations other than this, the following description isbased on the assumption that the transflector 141 according to thepresent embodiment is basically formed so as to entirely cover thesecond light-emitting surface 132 c of the light guiding plate 132 andto have two-dimensionally-uniform optical characteristics.

FIG. 2 illustrates example structures of the foregoing transflector 141.In the transflector having the example structure shown in FIG. 2( a), areflective thin film 141B composed of a reflective material, forexample, metal such as aluminum is formed on the front surface of atransparent substrate 141A composed of glass, a plastic film, or thelike. White pigment such as white resin and titanium oxide, metals suchas aluminum and silver, and so forth are preferred as the reflectivematerial. The transflector having this example structure may be formedsuch that the light guiding plate 132 is used instead of the foregoingtransparent substrate 141A and that the reflective thin film 141B isformed on the second light-emitting surface 132 c. This applies likewiseto the transflector having the other structures shown in FIGS. 2( b) to2(e).

By making a thin film from metal such as aluminum or silver so as tohave a thickness of about 10 nm to 50 nm, the reflective thin film 141Bhas an average transmittance of about 30% to 70% in a visible lightrange as its optical characteristic. The above thin film is formed bydeposition, sputtering, laser ablation, or the like. The reflectance andthe transmittance of the transflector having this example structure canbe adjusted by changing the film thickness.

Also, the transflector may be made from a known dielectric multilayerfilm instead of the reflective material as mentioned above.

In the transflector having the example structure shown in FIG. 2( b), areflective thin film 141C composed of a reflective material, forexample, metal such as aluminum is formed on the front surface of thetransparent substrate 141A. White pigment such as white resin andtitanium oxide, metal such as aluminum and silver, and so forth arenamed as the reflective material. The reflective thin film 141C isformed so as to have an average reflectance of about 90% or more as awhole in the visible light range and also to have a large number of fineapertures 141Ca formed therein. The fine apertures 141Ca are dispersedover the entire surface of the reflective thin film 141C. An equivalentaperture diameter of each fine aperture 141Ca, that is, an aperturediameter of a round aperture having the same area as that of the fineaperture, is preferably about 1 μm to 100 μm, and is more preferablyabout 5 μm to 30 μm. Especially, the fine apertures are preferablyformed so as to be smaller than the sizes of pixels of the first andsecond display units and also to be spaced at intervals smaller than thepitches of the pixels. The reflectance and the transmittance of thetransflector having this example structure can be adjusted by changingthe aperture area ratio of the fine apertures 141Ca. The aperture arearatio is determined by the equivalent aperture diameter and the formeddensity of the fine apertures 141Ca.

In the transflector having the example structure shown in FIG. 2( c), alight-diffusing layer 141D basically composed of a light transmissivematerial is formed on the front surface of the transparent substrate141A. The light-diffusing layer 141D includes a transparent substrate141 d 1 composed of acrylic resin or the like and fine particles 141 d 2dispersed in the substrate 141 d 1. The substrate 141 d 1 and the fineparticles 141 d 2 are composed of materials having different refractiveindexes from each other. Particles composed of silica, acrylic resin,and the like are named as the fine particles. The diameters of theparticles are preferably about 1 μm to 10 μm, and more preferably about4 μm to 5 μm.

In the transflector having this example structure, since the particleshaving different refractive indexes from each other are dispersed in thesubstrate, light is scattered or dispersed in a macroscopic view,whereby the transflector having this example structure exhibits opticalcharacteristics reflecting part of the light and transmitting theremaining light therethrough. The reflectance and the transmittance ofthe transflector having this example structure can be adjusted bychanging a difference in refractive indexes between the substrate andthe particles, the size and the distribution density of the particles,and the like.

In the transflector having the example structure shown in FIG. 2( d), alight-diffusing layer 141E basically composed of a light transmissivematerial is formed on the front surface of the transparent substrate141A. The light-diffusing layer 141E includes a transparent substrate141 e 1 composed of acrylic resin or the like and light reflective fineparticles 141 e 2 dispersed in the substrate 141 e 1. The fine particles141 e 2 are composed of a reflective material. White pigment such aswhite resin and titanium oxide, metal such as aluminum and silver, andso forth are preferred as the reflective material. The diameters of theparticles 141 e 2 are preferably about 1 μm to 10 μm, and morepreferably about 2 μm to 3 μm.

In the transflector having this example structure, since the particlescomposed of a reflective material are dispersed in the substrate, lightis scattered or dispersed in a macroscopic view, whereby thetransflector having this example structure exhibits opticalcharacteristics reflecting part of the light and transmitting theremaining light therethrough. The reflectance and the transmittance ofthe transflector having this example structure can be adjusted bychanging the reflectance, the size, and the density of the particles,and the like.

In the transflector having the example structure shown in FIG. 2( e),the reflective thin film 141B, the same as that shown in FIG. 2( a)composed of a reflective material, is formed on the front surface of thetransparent substrate 141A, and a diffusing layer 141F composed of alight transmissive material, preferably of a transparent material, andhaving fine undulations on the surface thereof is additionally formed onthe thin film 141B. The surface undulation of the diffusing layer 141Fhas a depth of about 2 μm to 3 μm formed at an interval of, for example,about 1 μm to 10 μm, preferably about 3 μm to 4 μm. This surfaceundulation is formed by patterning such as photolithography. Forexample, the above-mentioned surface undulation is formed such thatafter application on the reflective thin film 141B, a transparentphotosensitive resin is exposed with a mask pattern having openingsformed with an interval corresponding to the above-mentioned surfaceundulation and is then developed. Meanwhile, a step of additionallyapplying an additional transparent resin on the foregoing developedtransparent resin or heating the developed transparent resin so as to besoftened may be added so as to provide a smooth surface undulation.

According to this example structure, the transflector obtains reflectionand transmission characteristics in accordance with the thickness of thereflective thin film 141B in the same fashion as mentioned above, andalso is provided with a light-diffusing function since light incident onand reflected at the reflective thin film 141B is scattered by thediffusing layer 141F, thereby improving the evenness of the luminancedistributions of the first display unit 110 and the second display unit120.

Also, the light guiding plate 132 and the first display unit 110 have alight diffuser 142 interposed therebetween. The light diffuser 142 isintended to prevent the unevenness of display, that is, the unevenbrightness across the display surface of the fist display unit, causedby the structures of the light guiding plate 132 and the othercomponents lying on the back surface side thereof, that is, lying on thelower side in the figure, by appropriately diffusing light emitted fromthe light guiding plate 132. The light diffuser 142 may have an examplestructure in which fine particles composed of an acrylic resin or thelike and having an example diameter of about 2 μm to 3 μm are dispersedin a base material composed of an acrylic resin or the like having adifferent refractive index from that of the fine particles, or in whichfine undulations are provided on the surface thereof. More particularly,the light diffuser 142 may have the same structure as those shown inFIG. 2( c) or 2(d), or a structure formed by removing the reflectivethin film 141B from the structure shown in FIG. 2( e). The lightdiffuser 142 may be disposed while being bonded to the front surface ofthe light guiding plate 132 or may be formed from a sheet or a plateindependent of the light guiding plate 132.

Also, a light diffuser 145 is interposed between the light guiding plate132 and the second display unit 120, and is interposed between thetransflector 141 and the second display unit 120 according to thepresent embodiment. The light diffuser 145 has the same structure asthat of the light diffuser 142.

Meanwhile, in the present embodiment, since an overlapping portion,lying in a region two-dimensionally overlapping the display area of thefirst display unit 110 and two-dimensionally overlapping the displayarea of the second display unit 120, and the remaining portion lying inthe region have different optical structures from each other, in orderto improve the evenness of the display surface of the first displayunit, the foregoing light diffuser may be formed such that theoverlapping portion and the remaining portion have different diffusionrates, for example, haze values, from each other.

In the present embodiment, in order to increase the percentage of lightsubstantially contributing to display in each of the first display unit110 and the second display unit 120, light collectors 143 and 144, thatis, prism sheets 143 and 144 are interposed between the illuminationunit 130 and the first display unit 110, and light collectors 146 and147, that is, prism sheets 146 and 147 are interposed between theillumination unit 130 and the second display unit 120. Each lightcollector has a prism surface for refracting light so as to direct thelight along or close to an optical-axis direction of the display device,that is, the vertical direction in the figure. More particularly, theprism surface is formed by a plurality of ribs/convex portions, eachhaving a triangular cross section, juxtaposed with each other in astripe pattern on the surface of the corresponding collector. The lightcollectors 143 and 144 as well as the light collectors 146 and 147 aredisposed such that the foregoing corresponding ribs extend alongdirections substantially perpendicular to each other.

Next, an operation of the display device according to the presentembodiment and having the above-described structure will be described.In the following description, for simplicity of description, it isassumed that both the first display unit 110 and the second display unit120 serving as liquid crystal panels are formed so as to perform displayin a TN-type liquid crystal mode, that the polarizer 115 transmitslinearly polarized light A having a plane of vibration parallel to theplane of the figure, that is, first polarized light, and reflectslinearly polarized light B having a plane of vibration orthogonal to theplane of the figure, that is, second polarized light, and that thepolarizer 116 transmits the linearly polarized light B, that is, thirdpolarized light, and absorbs the linearly polarized light A, that is, afourth polarized light. In addition, it is assumed that the polarizer125 transmits the linearly polarized light A and absorbs the linearlypolarized light B, and that the polarizer 126 transmits the linearlypolarized light B and absorbs the linearly polarized light A. That is,although directional relationships among the planes of vibration of thefirst polarized light to the fourth polarized light are generallyarbitrary, in the following description, the first polarized light andthe fourth polarized light exhibit the same polarized state as eachother, and the second polarized light and the third polarized lightexhibit the same polarized state as each other.

Light emitted from the light source 131 is introduced in the lightguiding plate 132 and is emitted little by little therefrom towards thefront and back surface sides while propagating in the light guidingplate 132. First, illumination light emitted towards the first displayunit 110 passes through the light diffuser 142, becomes the linearlypolarized light B upon passing through the polarizer 116, passes throughthe light collectors 143 and 144, and is then incident on the liquidcrystal 114. When the liquid crystal 114 is in an OFF-state, uponpassing through the liquid crystal 114, the illumination light becomesthe linearly polarized light A due to the optical rotary power of theliquid crystal, passes through the polarizer 115, and is emitted towardsthe front surface side as transmissive light T1. When the liquid crystal114 is in an ON-state, since the illumination light remains as thelinearly polarized light B even when passing through the liquid crystal114, it is absorbed by the polarizer 115.

In the meantime, external light incident on the first display unit 110becomes the linearly polarized light A upon passing through thepolarizer 115 and is incident on the liquid crystal 114. When the liquidcrystal 114 is in an OFF-state, the external light becomes the linearlypolarized light B, is transmitted through the polarizer 116, and entersthe light guiding plate 132, and then, part of this light is reflectedat the transflector 141, becomes the linearly polarized light A uponpassing again through the polarizer 116 and the liquid crystal 114, istransmitted through the polarizer 115, and is emitted as reflectivelight RD1. Also, when the liquid crystal 114 is in an ON-state, sincethe linearly polarized light A of the external light passing through thepolarizer 115 remains as the linearly polarized light A even whenpassing through the liquid crystal 114, it is absorbed by the polarizer116.

Meanwhile, when the foregoing light collectors 143 and 144 are disposed,since external light is scattered upon being incident on these lightcollectors, the reflective light RD1 is not substantially obtained.Accordingly, when it is expected to effectively use the foregoingreflective light RD1, it is preferable that none of these lightcollectors be disposed.

Next, part of illumination light emitted from the illumination unit 130towards the second display unit 120 is transmitted through thetransflector 141, passes through the light diffuser 145, becomes thelinearly polarized light B upon passing through the polarizer 126, andpasses through the liquid crystal 124. When the liquid crystal 124 is inan OFF-state, upon passing through the liquid crystal 124, the linearlypolarized light B becomes the linearly polarized light A, is transmittedthrough the polarizer 125, and is emitted as transmissive light T2towards the back surface side. When the liquid crystal 124 is in anON-state, since the linearly polarized light B remains as it is evenwhen passing through the liquid crystal 124, it is absorbed thepolarizer 125.

In the meantime, of external light incident on the second display unit120, the linearly polarized light A is transmitted through the polarizer125 and is incident on the liquid crystal 124. When the liquid crystal124 is in an OFF-state, the linearly polarized light A becomes thelinearly polarized light B and passes through the polarizer 126 and thelight diffuser 143, and then, part of this light is reflected at thetransflector 141 while other part of the light is introduced in thelight guiding plate 132. The linearly polarized light B reflected at thetransflector 141 passes through the light diffuser 145 and the polarizer126 as it is, becomes the linearly polarized light A upon passing againthrough the liquid crystal 124, is transmitted through the polarizer125, and is emitted as reflective light RD2. When the liquid crystal 124is in an ON-state, since the above-mentioned linearly polarized light Aremains as it is even when passing through the liquid crystal 124, it isabsorbed by the polarizer 126.

Meanwhile, when the foregoing light collectors 146 and 147 are disposed,since external light is scattered upon being incident on these lightcollectors, the reflective light RD2 is not substantially obtained.Accordingly, when it is expected to effectively use the foregoingreflective light RD2, it is preferable that none of these lightcollectors be disposed.

As described above, in the present embodiment, the first display unit110 performs display with the transmissive light T1 and the reflectivelight RD1. Also, the second display unit 120 performs display with thetransmissive light T2 and the reflective light RD2. The presence of thereflective light RD1 and the reflective light RD2 prevents deteriorationin visibility of display in the case of observing an object at a brightplace like outdoors or in the case of cutting an amount of illuminationlight of the illumination unit 130.

In the present embodiment, the illumination unit 130 is formed so as toemit light towards both the first display unit 110 and the seconddisplay unit 120, and in particular, the light guiding plate 132interposed between the first display unit 110 and the second displayunit 120 is shared by them, thereby making the overall structure of thedisplay device 100 thin and light. Also, with the transflector 141disposed as mentioned above, light in the light guiding plate 132 can bedivided towards both the first display unit 110 and the second displayunit 120 respectively disposed on the front and back sides, the evennessof illumination light emitted from the light guiding plate 132 towardseach of the front and back sides can be improved, and also, externallight incident on the first display unit 110 and the second display unit120 can be reflected at the transflector so as to serve as part ofdisplay light.

In particular, with the presence of the transflector 141, theilluminance distribution of the illumination unit 130 on the firstdisplay unit 110 is unlikely to be optically affected by the presence ofthe second display unit 120. With this structure, even when the displayarea of the first display unit 110 is set greater than that of thesecond display unit 120 as shown in the figure, a shadow of the displayarea of the second display unit 120 is unlikely to be reflected in thedisplay surface of the first display unit 110, thereby improving thedisplay quality of the first display unit 110.

Meanwhile, as mentioned above, although the display areas of the firstand second display units 110 and 120 overlap with each other, in thecase where the one includes the other or in the case where the twodisplay areas do not partially overlap with each other, the unevennessof display becomes generally noticeable. Hence, the above-describedstructure is especially effective in these cases. However, regardless ofthe above-mentioned cases, when a common illuminator is used toilluminate the display units lying on both the front and back sides, theunevenness of the illuminance distribution of the illumination unit isin general likely to occur. Hence, different from the above cases, evenwhen both the display areas have almost the same size as each other andoverlap so as to align two-dimensionally with each other, the structureof the display device according to the present invention is technicallyeffective in order to achieve the evenness of the luminance of each ofthe display units.

Second Embodiment

Referring next to FIG. 3, a display device according to a secondembodiment of the present invention will be described. Since the displaydevice according to the second embodiment basically has the samestructure as that of the display device according to the firstembodiment shown in FIG. 1 except for its transflector, illustrationsand descriptions of the same parts in the second embodiment will beomitted.

As shown in FIG. 3( a), a transflector 241 according to the presentembodiment is interposed between the second light-emitting surface 132 cof the light guiding plate 132 and the second display unit 120 so as toentirely cover a region AR1 two-dimensionally overlapping the displayarea of the first display unit 110. The transflector 241 has anoverlapping portion AR2 which two-dimensionally overlaps the displayarea of the second display unit 120 and which serves as an aperture241A, and in the region AR1, a portion AR3 other than the overlappingportion AR2 serves as a reflector 241R reflecting visible light.

With this structure, the second display unit 120 is illuminated withlight emitted from the light guiding plate 132 and passing through theaperture 241A, thereby easily achieving bright display of the seconddisplay unit 120. Also, with respect to the first display unit 110,since substantially all light is reflected at the portion AR3, an amountof light contributing to display as a whole can be increased. However,in this case, since the intensity of the illumination light illuminatingthe first display unit 110 decreases in the overlapping portion AR2, itis preferable that the display device preferably have a structure inwhich the intensity distribution of the illumination light can bemodified by adjusting a light-diffusing effect of the light diffuser142, a light-emitting distribution of the light guiding plate 132, andthe like.

FIG. 3( b) illustrates a modification of the present embodiment. Atransflector 241′ according to the modification is formed such that alarge number of fine apertures 241A′ are dispersed in the reflectivesurface of the overlapping portion AR2 and that a portion other than theoverlapping portion AR2 has no apertures and serves as the reflector241R′ reflecting light. In this modification, the second display unit120 is illuminated with light passing through the fine apertures 241A′formed in the overlapping portion AR2. However, in the overlappingportion AR2, since light is reflected at the reflective surface otherthan the fine apertures 241A′ towards the first display unit 110, adifference in brightness of display between two parts of the displaysurface of the first display unit 110 respectively corresponding to theoverlapping portion AR2 and the remaining portion AR3 can be reduced.Meanwhile, also in this case, in order to further prevent the unevennessof display of the first display unit 110, it is preferable that thedisplay device have a structure in which the intensity distribution ofthe illumination light can be modified by adjusting a light-diffusingeffect of the light diffuser 142, a light-emitting distribution of thelight guiding plate 132, and the like.

Third Embodiment

Referring next to FIG. 4, a display device according to a thirdembodiment of the present invention will be described. Since the displaydevice according to the present embodiment basically has the samestructure as that of the display device according to the firstembodiment shown in FIG. 1 except for its transflector, illustrationsand descriptions of the same parts in the third embodiment will beomitted.

As shown in FIG. 4( a), in the region AR1, a transflector 341 is formedsuch that the overlapping portion AR2 is composed of a transflectivematerial 341A having a predetermined reflectance and transmittance, forexample, both in the range from 30 to 70%, and the portion AR3 otherthan the overlapping portion AR2 is composed of a reflective material341B having a lower transmittance than that of the overlapping portionAR2 while having substantially the same reflectance as that of theoverlapping portion AR2, for example, in the range from 30 to 70%. It ispreferable that the transmittance of the reflective material 341B of theportion AR3 be nearly 0%. Such a material is easily obtained, especiallyfrom a dielectric multilayer film.

With this structure, the overlapping portion AR2 in the region AR1allows illumination light emitted from the illumination unit 130 to bereflected towards the first display unit 110 and to be transmittedtherethrough towards the second display unit 120 at the same time,whereby both display units can be illuminated at the same time. Inaddition, the portion AR3 other than the overlapping portion AR2 doesnot allow unnecessary light to be transmitted therethrough towards theback thereof because of its low transmittance, and also, since thereflectance of the portion AR3 is substantially the same as that of theoverlapping portion AR2, the unevenness of display of the first displayunit 110 can be prevented.

According to this example structure, when it is intended to remove theunevenness of display of the first display unit 110, a light loss ofillumination light due to absorption by the portion AR3 is generated,whereby a light utilization efficiency of the display device as a wholedecreases. In order to improve the light utilization efficiency, it isnecessary to reduce the light loss in the portion AR3 by making thereflectance of the portion AR3 higher relative to that of theoverlapping portion AR2, and it is preferable that the unevenness ofdisplay of the first display unit 110 possibly caused by thisarrangement be modified by changing the structures of the light-guidingplate 132, the light diffuser 142, and so forth.

FIG. 4( b) illustrates a modification of the present embodiment. Anentire transflector 341′ is composed of a reflective material. Thetransflector 341′ has a large number of fine apertures 341A′ dispersedin the overlapping portion AR2, and, in place of the fine apertures341A′, also has fine absorbers 341B′ composed of a black resin or thelike and dispersed in the portion AR3 other than the overlapping portionAR2.

The transflector 341′ has a structure in which the fine apertures 341A′in the overlapping portion AR2 allow the second display unit 120 lyingat the back thereof to be illuminated with light, and also the fineabsorbers 341B′ formed in the remaining portion AR3 reduce a differencein reflectances between the overlapping portion AR2 and the portion AR3.With this structure, the unevenness of display of the first display unit110 can be prevented.

Fourth Embodiment

Referring next to FIG. 5, a display device according to a fourthembodiment of the present invention will be described. The displaydevice according to the present embodiment has a structure in which anyone of the display devices according to the foregoing embodiments isaccommodated in a casing composed of a synthetic resin, or the like.Accordingly, since the display device of the present embodimentbasically has the same structure as that of the display device accordingto the first embodiment shown in FIG. 1 except for its structuralfeature of accommodation with the casing, illustrations of the sameparts in the present embodiment will be simplified and descriptions ofthe same parts will be omitted.

As shown in FIG. 5( a), a display device 100′ includes the first displayunit 110, the second display unit 120, the illumination unit 130, andthe other foregoing components (not shown), which are the same as thoseof each of the display devices according to the foregoing embodiments,and these components are accommodated in a casing 150. The casing 150 iscomposed of, for example, a white synthetic resin. Making the casing 150from a white material is preferable from the viewpoint of improving autilization efficiency of illumination light of the illumination unit130 since this casing reflects light leaked from the light guiding plate132 and returns again to the light guiding plate 132.

In the present embodiment, an area not having the second display unit120 disposed therein, on the front surface of the second light-emittingsurface of the light guiding plate 132 of the illumination unit 130,that is, the foregoing portion AR3, has an optical sheet 151 havingpredetermined optical characteristics and disposed therein. When viewedfrom the first display unit 110, the optical sheet 151 is composed of amaterial having substantially the same reflectance as that of the seconddisplay unit 120. With this structure, even when the transflector 141has entirely uniform optical characteristics, the unevenness of displayof the display surface of the first display unit can be decreased.

FIG. 5( b) illustrates a modification of the present embodiment. In adisplay device 100″ according to this modification, the first displayunit 110, the second display unit 120, the illumination unit 130, andthe other components (not shown), which are the same as those of each ofthe display devices according to the foregoing embodiments, areaccommodated in a casing 160. When viewed from the first display unit110, the casing 160 is composed of a material exhibiting substantiallythe same reflectance as that of the second display unit 120. With thisstructure, even when the foregoing transflector 141 has entirely uniformoptical characteristics, the unevenness of display of the displaysurface of the first display unit can be decreased.

Meanwhile, the optical sheet 151 and the casing 160 suffice to be formedsuch that, when observed from the first display unit 110 via theillumination unit 130, the illuminance distributions of a portion wherethe display area of the second display unit 120 presents and anotherportion where the optical sheet 151 and the casing 160 are disposed aremutually made uniform regardless of the structures of the transflector141 and the light guiding plate 132.

Fifth Embodiment

Referring next to FIGS. 6 and 7, an electronic apparatus, including thedisplay device 100 according to the first embodiment, will be described.As shown in FIG. 6, the electronic apparatus according to the presentembodiment includes a controller 1100 for controlling the first displayunit 110, that is, the liquid crystal display panel 110, and acontroller 1200 for controlling the second display unit 120, that is,the liquid crystal display panel 120. The controllers 1100 and 1200 arecontrolled by a central controller 1000 disposed in the electronicapparatus and formed by a microcomputer and so forth.

The first and second display units 110 and 120 are respectivelyconnected to drive circuits 110D and 120D including semiconductor ICsand the like, which are mounted on the corresponding panels or connectedto the corresponding panels via respective wiring members, and thesedrive circuits 110D and 120D are respectively connected to thecontrollers 1100 and 1200. The controllers 1100 and 1200 respectivelyinclude display-information output sources 1110 and 1210,display-information process circuits 1120 and 1220, power supplycircuits 1130 and 1230, and timing generators 1140 and 1240.

Each of the display-information output sources 1110 and 1210 includes amemory such as a read only memory (ROM) and/or a random access memory(RAM), a storage unit such as a magnetic storage disk and/or an opticalstorage disk, and a tuning circuit for outputting a tuned digital imagesignal. Also, in response to a variety of clock signals generated by thetiming generators 1140 and 1240, the display-information output sources1110 and 1210 supply display information, in the form of an image signalaccording to a predetermined format or the like, to thedisplay-information process circuits 1120 and 1220, respectively.

Each of the display-information process circuits 1120 and 1220 includesa variety of known circuits such as a serial-parallel conversioncircuit, an amplification and reversion circuit, a rotation circuit, agamma correction circuit, and a clamp circuit, processes the inputdisplay information, and supplies the processed image informationtogether with a clock signal CLK to the corresponding drive circuit.Each of the drive circuits 110D and 120D includes a scan-line drivecircuit, a data-line drive circuit, and a testing circuit. Also, each ofthe power supply circuits 1130 and 1230 supplies a predetermined voltageto each of the above described corresponding components.

The central controller 1000 sends original data for illuminationlights-on and -off commands and display information, and the like, ifneeded, to the display-information output sources 1110 and 1210 of thecorresponding controllers 1100 and 1200, controls thedisplay-information output sources 1110 and 1210 so as to output displayinformation in response to the original data and the like, and alsocontrols the first display unit 110 and the second display unit 120 soas to display required display images via the controllers 1100 and 1200and the drive circuits 110D and 120D, respectively. Also, the centralcontroller 1000 is formed so as to control the illumination lights-onand -off, and the like of the light source 131.

FIG. 7 illustrates a cellular phone 2000 serving as an example of theelectronic apparatus according to the present invention. The cellularphone 2000 includes a main body 2001 having a variety of buttonsdisposed thereon and a microphone housed therein, and a display unit2002 having a display screen and an antenna mounted thereon and aspeaker housed therein, and the main body 2001 and the display unit 2002are constructed so as to be mutually foldable. The display unit 2002 hasthe display device 100 housed therein, while having the display screenof the first display unit 110 disposed on the inner surface thereof soas to be visible and also the display screen of the second display unit120 disposed on the outer surface thereof so as to be visible.

In the present embodiment, as shown in FIG. 7( a), when the display unit2002 is opened by separating from the main body 2001, in response to acommand from the central controller 1000, the first display unit 110 isilluminated, and a predetermined image is displayed. Also, as shown inFIG. 7( b), when the display unit 2002 is folded onto the main body2001, the first display unit 110 is illumination lights-off, the seconddisplay unit 120 is illuminated instead of the above illuminationlights-off, and a predetermined image is displayed.

In the present embodiment, the display device 100 having a thinstructure as mentioned above allows the display unit 2002 to have a thinstructure, to have a simple internal structure, and to be easilyassembled. Meanwhile, the electronic apparatus according to the presentembodiment may also have any one of the display devices in the second tofourth embodiments mounted thereon.

Meanwhile, the electro-optical device and the electronic apparatusaccording to the present invention are not limited to the foregoingexample illustrations, and those skilled in the art will appreciate thata variety of modifications can be possible without departing from thespirit of the present invention. For example, although a liquid crystaldisplay panel is used as an electro-optical panel in each of theforegoing embodiments, any one of a variety of electro-optical panelssuch as an organic electro-luminescence panel, a plasma display panel,and a field-emission display panel may also be used as theelectro-optical panel according to the present invention. Also, althoughthe liquid crystal display panel of a passive matrix type is basicallyillustrated in the foregoing embodiments, the present invention islikewise applicable to that of an active matrix type.

The entire disclosure of Japanese Patent Application No. 2002-316081filed Oct. 30, 2002 is incorporated by reference.

1. A display device, comprising: a first display unit having a displayarea; a second display unit having a display area facing in an oppositedirection than the display area of the first display unit, the displayarea of the second display unit being smaller than the display area ofthe first display unit; an illumination unit disposed between the firstdisplay unit and the second display unit and illuminating light ontoboth the first display unit and the second display unit, theillumination unit including a light guide member having a first lightemitting surface facing the first display unit and a second lightemitting surface facing away from the first light emitting surface; andan optical sheet disposed at the second light emitting surface of theillumination unit at a position that is in an overlapping condition withthe display area of the first display unit in plan view and is in anon-overlapping condition with the display area of the second displayunit in plan view.
 2. The display device of claim 1, further comprisingan aperture disposed within the optical sheet, the second display unitbeing located in the aperture.
 3. The display device of claim 1 wherein:outer edges of the second display unit are inboard of outer edges of thefirst display unit.
 4. A display device comprising: a first display unithaving a display area; a second display unit having a display area thatis smaller than the display area of said first display unit; anillumination unit between said first display unit and said seconddisplay unit; an optical sheet that overlaps the display area of saidfirst display unit in plan view and does not overlap the display area ofsaid second display unit in plan view; and wherein said optical sheetincludes an aperture, and the display area of said second display unitis aligned with said aperture.
 5. The display device of claim 4, whereinsaid optical sheet has at least substantially the same reflectance assaid second display unit.
 6. The display device of claim 4, wherein saidfirst display unit overlaps said second display unit as well as a regionbeyond said second display unit.
 7. A display device comprising: a firstdisplay unit; a second display unit that is smaller than the firstdisplay unit; an illumination unit between said first display unit andsaid second display unit; and an optical sheet that overlaps with thefirst display unit in plan view, the optical sheet having an aperture,at least a portion of said second display unit overlapping said firstdisplay unit through the aperture in said optical sheet.
 8. A cellularphone comprising: the display device of claim
 7. 9. The display deviceof claim 7 further comprising a casing having at least a white innersurface, with a side wall of the casing confronting a side edge of theillumination unit.
 10. The display device of claim 7 wherein: outeredges of the second display unit are inboard of outer edges of the firstdisplay unit.
 11. A display device comprising: a first display unit; asecond display unit that is smaller than said first display unit; anillumination unit between said first display unit and said seconddisplay unit; and an optical sheet that overlaps with said first displayunit in plan view, said optical sheet having an aperture at a positionthat corresponds to the position of said second display unit.
 12. Acellular phone comprising: the display device of claim
 11. 13. Thedisplay device of claim 11 further comprising a casing having at least awhite inner surface, with a side wall of the casing confronting a sideedge of the illumination unit.
 14. The display device of claim 11wherein: outer edges of the second display unit are inboard of outeredges of the first display unit.
 15. A display device comprising: afirst display unit with two outer peripheral edges of opposite endsthereof; a second display unit with two outer peripheral edges onopposite ends thereof, the two outer peripheral edges of said seconddisplay panel being inboard of the two outer peripheral edges of saidfirst display unit; an illumination unit between said first display unitand said second display unit; and an optical sheet with two outerperipheral edges on opposite ends thereof, the two outer peripheraledges of said optical sheet being outboard of the two outer peripheraledges of said second display unit, said optical sheet having an apertureinboard of the two outer peripheral edges of said first display unit, atleast a portion of said second display unit facing said first displayunit through the aperture in said optical sheet.
 16. A cellular phonecomprising: the display device of claim
 15. 17. The display device ofclaim 15 further comprising a casing having at least a white innersurface, with a side wall of the casing confronting a side edge of theillumination unit.